Turbine blade cooling structure



Feb. 5, 1957 T. w. JACKSON 2,780,435

TURBINE BLADE COOLING STRUCTURE Fi1 ed Jam. 12, 1955 A lit mi! T hopuisWJ dlwom await/ax United States Patent ce 2,780,435 TURBINE BLADECOOLING STRUCTURE Thomas Woodrow Jackson, Cincinnati, Ohio, assignor tothe United States of America as represented by the Secretary of the NavyApplication January 12, 1953, Serial No. 330,931

Claims. (Cl. 25339.15)

(Granted under Title 35, U. S. Code (1952), see. 266) This inventionrelates to turbine blades and the like with particular reference to thecooling of the leading edges thereof In turbine blades subject to highgas-to-blade heat transfer with resultant corrosion and erosion of theblade metal, it becomes of considerable importance to provide effectivemeans for cooling the leading edges. A cooling method heretofore usedconsists in attaching a displaced strip over the leading edge andpassing air to the edge and strip through slots cut in the blade edge. Adifficulty of this methodlies in the pronounced pressure reduction ofthe air flow due to the slot area, thus reducing the cooling effect onthe strip to the danger point. To overcome this deficiency, fins areinserted in the slots but their use involves difficulty in manufacture.An added deficiency in the use of slots for cooling lies in theweakening elfect on the metal structure especially where it is necessaryto use nonstrategic alloys.

A primary object of the present invention is to provide a blade coolingdevice which, while effectively cooling the blade edge, will not impartweakness to the blade structure. A further object is to insure adequatecontrol over corrosion and erosion in turbine blades subject to hightemperature gas flow. Still another object is to supply coolingarrangements such as will permit use of nonstrategic metals in turbineblade construction.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, wherein:

Fig. 1 is a view of the improved blade in perspective with parts cutaway to show the blade construction;

Fig. 2 is a detailed perspective view of the blade leading edge with thecap broken away to show the blade holes and lateral grooves; and

Fig. 3 is a sectional detail of the blade leading edge and cap plate.

Referring to Fig. 1 there is disclosed a turbine blade unit of the axialflow type consisting of the blade 11 and blade root 12. These two bladeelements as here shown consist of a single integral member. The blade ishollow and is fashioned as an air foil with concaveconvex sides 5 and 6,a somewhat broadly rounded leading edge 8 and a sharpened trailing edge9. The tip end 13 of the blade includes a plate 14 provided with anarcuate opening 15 therein extending over the greater portion of the tiparea, the plate section 16 adjacent the leading edge being closed.

The blade root 12 is an extension of the blade and is formed in wedgeshape with the blade integral with the blunt end 18 of the wedge and theside walls of the wedge formed with lateral ribs 19 to form a slidingengagement with correspondingly shaped receiving spaces in the turkbinehub.

Radially positioned in the hollow interior of the blade 2,780,435Patented Feb. 5, V 1957 are a group of tubes 25 forming passagesparallel to the longitudinal axis of the blade for carrying coolanttherethrough and means for connecting said tubes to a source of coolant.The tubes which are shown in Fig. I extend from openings in the tipplate 14 to an arcuate opening or tube 26 in the root. This latteropening communicates through hub ducts to a source of air pressure. Thepurpose of the tubes 25 is to supply cooling air to the blade interiorso that by cooling the tube walls the entire blade is cooled. Theleading tube 25a (Fig. 3) is oversized to form a sealing barrier betweenthe blade walls, thereby providing a closed forward chamber 27 in theblade.

Since the leading blade edge is subjected to highest heat effects,special cooling means are required to prevent excessive heat erosion andcorrosion in this area. To this end the forward blade edge is perforatedby a series of air ducts 30 which are alined radially with reference tothe blade root and centrally or medially along the blade leading edgeand which thus extend between the blade exterior and the interiorforward chamber 27 of the blade; and the leading edge material laterallyof each duct 30 and transversely of the blade edge is grooved, as bestshownin Figs. 2 and 3, to form side channels 31 which serve .as guidesto air flow for air moving outwardly through ducts 30.

Surmounting the leading edge and secured thereto centrally along themedian line joining the ducts 30, is a blade-length U-shaped sessile cap33, the skirts or walls 34 thereof being tapered in section to a thinedge 34a. This cap is fixed solidly to the leading edge, as by spotwelding, at the raised points between the ducts 30, the side skirts orwalls overlying the transverse channels 31 and a limited portion of theblade side walls 5 and 6 beyond these channel ends, thus forming lateralducts from the :outlet ends of ducts 30. The curvature of the cap islesser than that of the leading edge 8 so that with the cap attached insymmetrical relation to the blade, the cap skirts or walls divergeoutwardly to form an increasing exit space for air passage from theouter openings of the ducts 30 to the cap edges. The channels 31 thusserve to provide direction reversing deflection of the air at theleading edge and to accelerate the air flow in the ducts 30, thereby toprovide maximum cooling at the blade areas subjected to maximum heat. Itis pointed out that the cap skirts 34, as shown in Fig. 1, are ofuniform length along the blade and that the channels 31, as shown inFig. 2, are of approximately equal length. Hence, the lateral ductsformed by the cap skirts and channels are of approximately equal length.

In operation, air from any appropriate pressure source is fed to the hubmanifold (not shown) and thence to the blade root tube 26. From tube 26the air flows to the tubes 25, the forward chamber 27 and ducts 30. Thecompressed air emitted from ducts 30 impinge on the cap 33 and isreversely turned through channels .31 to be discharged beyond the capwall edges. The air reversal under pressure in contact with the caprapidly withdraws heat from the cap and the cap in turn absorbs heat byconduction and radiation from the blade edge. Considerable convectioncooling also takes place at the blade and cap surfaces. The tapered capwalls or skirts reduce the heat reservoir action thereof withoutaffecting the air channelling action.

Obviously modifications and variations of the invention as disclosed arepossible and it is to be understood therefore within the scope of theappended claims the invention may be practiced otherwise than asspecifically described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

blade -root* and'-' connectingisaid charnber to a sourceof coolant, aplurality-"ofoutwardly directed ducts formed througlrthe: leading edge:of said blade-andextending from said chamber tothe blade :exterior, aplurality of surface-grooves on .the leading edge=of said: bladeextending transversely'fromv either side of the outer end of each' ofsaid ducts -to fortncoolant channels, and an elongated sessile capattached-t said 1 blade edge and overlying said: channels. to formtransverse ducts, said cap having side" skirts forming: :1: directionreversing deflector for coolantflowing out of said outwardly extendingduets? 2; Thebla'de coolingsd'evice. asdefinedv in claim 1, said bladehaving therein a pluralityof axially parallelipassageways con'nected tosaid bladeroot tube for carrying coolant through-said blade.

3; A cooling-device fortheleading edge of a turbine bladecomprisinga-turbine blade having a leading edge, a sessile cap fixed along saidleading edge having reversed side skirtsextendingover andspaced from thesides of said leading edge to form side spaces, a chamber withinsaidblade adjacent said-edge adaptedto receive coolant, a plurality ofducts alined centrally along said leading edge connecting said. chambertothe outer edge surface inside said cap, and lateral ducts formed inthe leading edge surface connecting said central ducts to the saidspaces betweemsaid blade and cap side skirts, whereby coolant suppliedsaid chamber will move through said ducts against said cap and inreverse direction along said cap skirts.

4. The cooling device for blade edges as defined in claim 3, saidlateral ducts consisting of surface grooves of approximately equallength in the blade edge surface from the central duct outlets to apointshort of the trailing edge of said side.skirts on,..both sidesofsaidblade edge, whereby said lateral ducts are of approximately equallength.

5 A cooling device for blade edgescompris'inga bladelength leading bladeedge of a givencurvature, abladelength reversely curved cap attachedvmedially, along, said edge and having rearwardly directed skirtsoverlying and displaced from theside-surfaces of'said edge and forming adischargev space .with said leadingedge and.apluraiity of radial ductsformed medially through said edge for supplying coolant to the rearwardsurface of said cap, said blade edge having lateral ducts connectingeach of said radial ducts to the spaces between said, cap. side skirtsand said bladeand said rearwardcap surface having a curvature lesserthan that of'said blade edge, whereby the discharge space between capand blade, increases progressively from forward to rearward.

References Cited in the file of this=patent UNITED STATES PATEI-ITS2,220,420 Meyer Nov. 5,,1940. 2,236,426 Faber Mar. 25, 1941. 2,585,871Stalker Feb. 12, 1952, 2,613,911 Clarke Oct. 14, 1952,

